JSFiddle - React, Tailwind, and code Playground

HTML

<input name="dddddd">
<input name="dddddd[5][ssss]">
<input name="dddddd[][sssss]">
<input name="dddddd[ssss][25]">
<input name="dddddd[ssssss]">
<input name="dddddd[][5]">

JavaScript

jQuery(function($) {
  $('input').each(function(i) {

    var $obj = $(this).attr('name'),
      $pattern = new RegExp('/\[\d{1,4}\]/g');
    $(this).val($obj);
    if ($pattern.test($obj)) {
      $(this).val(i);
    }

  });
});